DESCRIPTION: The principal investigator proposes to characterize the cells which give rise to the principle neurons and glial cells in a post- migratory neural crest population. Both cloning and dye injection studies suggest that early neural crest cells are multi-potent. However, once neural crest cells coalesce to form a rat sympathetic ganglion, they appear to be committed to neuronal or glial cell fates. The first specific aim will ask whether this cell commitment is a common feature of another neural crest derivative, the sensory ganglion. The Principal Investigator will introduce a retroviral lineage marker into dissociated cells and ask if single cells give rise to both neurons and glia. The second specific aim will address factors proposed to regulate the differentiation of two neural cell types in sympathetic ganglia, principal neurons and small, intensely fluorescent (SIF) cells. Both neural types are generated prenatally within the same ganglionic environment, glucocorticoids have been proposed to regulate their differentiation. How these potentially molecular signals are segregated to produce both types of cells is uncertain. One difference between these cells during embryonic development is that SIF cells mature opposed to blood vessels. The Principal Investigator will ask if components of endothelial cells in addition to NGF precursors. In addition, because sympathetic ganglia form adjacent to the notochord on the establishment of the adrenergic phenotype in chick peripheral ganglia.